Hematopoietins or hematopoietic growth factors are proteins that promote the survival, growth and differentiation of hematopoietic cells. The biochemical and biological identification and characterization of certain hematopoietins has been hampered by the small quantities of the factors available from natural sources, e.g., blood and urine. With recombinant genetic engineering techniques, however, some of these hematopoietins have been molecularly cloned, heterologously expressed and purified to homogeneity. Among these hematopoietins are colony stimulating factors (CSFs) characterized by the ability to support the growth in vitro of colonies of hematopoietic cells arising from progenitor cells of bone marrow, fetal liver and other organs, e.g. GM-CSF, G-CSF, CSF-1 and IL-3. [See, e.g., D. Metcalf, Blood, 67(2): 257-267 (1986); Y. C. Yang et al, Cell, 47(1):3-10 (1986); R. Donahue et al, Nature, 321:872-875 (1986)].
Subsequent to the filing date of the present inventors' United States priority applications, several publications issued by other researchers describing proteins characterized by other biological activities and names, which were identical to the novel protein, called IL-6 described herein and in the priority applications. See, Haegeman et al, Eur. J. Biochem., 159:625-632 (1986) and references cited therein [the 26 kd protein inducible in human fibroblasts]; Zilberstein et al, EMBO J., 5:2529-2537 (1986) [IFN-beta-2 with weak interferon activity]; and Hirano et al, Nature, 324:73-76 (1986) [BCDF or BSF-2 for its B cell stimulatory activity]. See also, published European Patent Application 220,574. Several of these papers reported purification of the natural substance.